123 

 A summary of selected major fragmentations of dimers and associated 



attachments is presented in figure 3-10. This figure is arranged such that reactions 



involving lactate, or the lactate-lactic acid dimer are found towards the top left 



corner of the diagram; those involving the Hj-eliminated analogs of these species 



are found towards the bottom right corner. 



The similarity in fragmentations of m/z 179 and m/z 177 is clearly evident. 

 Both species undergo neutral losses of CO2 to form ions which can then cleave the 

 remainder of the neutral lactic acid molecule to form ions at m/z 89 and m/z 87 

 depending on the initial dimeric species. Both the m/z 179 and m/z 177 dimer can 

 form ions at m/z 89 and m/z 87. Additionally, both neutral lactic acid (90 Da) and 

 the H2-eliminated lactic acid neutral (88 Da) can form chloride attachment ions. 



Differences are found in the fragments of the dimer ions. The m/z 179 dimer 

 ion can undergo a neutral loss of CO and a neutral loss of HjO. The intensities of 

 fragment ions formed by identical losses from the m/z 177 dimer ion fall below the 

 threshold percentage (1% base peak) chosen for presentation. An additional dimer 

 ion at m/z 175 formed from the association of Hj-eliminated lactate and lactic acid 

 fragments to yield only m/z 87; this is also not presented in the figure. The only 

 significant fragment ion arising from the m/z 177 dimer (with exception of m/z 89 

 and m/z 87) is due to the neutral loss of CO2, forming the m/z 133 ion. 



Lastly the issue of dimer formation in the NCI mass spectrum of lactic acid 

 just prior to and after saturation of the ion source can be addressed and illustrated 

 by examining figures 3-11 and 3-12. Figure 3-11 depicts the m/z 87 ion in greater 



